The present invention relates to a semiconductor device, in particular, to that with a layered interconnect structure.
In recent large-scale-integration, high-performance semiconductor devices, copper (Cu) interconnects are being employed as having lower electric resistance than conventional aluminum (Al) interconnects. However, diffusion of copper (Cu) atoms into silicon (Si) substrates or insulating films will detract from the characteristics of the devices. To prevent the copper (Cu) diffusion, a diffusion barrier is formed adjacent, to the copper (Cu) film. As the material for the diffusion barrier, high-melting-point metal films of, for example, titanium nitride (TiN), tungsten (W) or tantalum (Ta) have been investigated, as in the Nikkei Microdevice (for July 1992, pp. 74-77).
Large-scale-integration semiconductor devices with fine patterns receive high-density current, in which, therefore, atoms are diffused owing to electron streams flowing therein and to heat as generated by the flow to cause voids and interconnect breakdowns. The problem with the devices is so-called electromigration. As compared with aluminum (Al) films, copper (Cu) films, as having a higher melting point, are difficult to diffuse, and are therefore expected to have good electromigration resistance. However, layered interconnect structures in which a diffusion barrier of, for example, a titanium nitride (TiN) film, a tungsten (W) film or a tantalum (Ta) film is kept in contact with a copper (Cu) film could not have satisfactory electromigration resistance, and therefore often pose the problem of voids and interconnect breakdowns.